When drilling is performed in hard materials and at high a speed it is customary to provide a fluid for cooling and/or lubrication through the drill bit. Such cooling and lubrication is important to guarantee the quality of the drilling and to minimise the wear of the drilling equipment.
One manner of achieving the cooling and lubrication in a pneumatic tool is to utilise the pressurised air that is provided to the system for driving the motor to produce a mist or fluid from a combination of pressurised air and a lubricator. Another conventional way is to provide a cooling and/or lubrication fluid from an external system. Either way the cooling and/or lubrication fluid is provided through the rotating spindle and into the interior of the drill bit via an interface between the spindle and the drill bit.
A problem with such internal fluid conduction is that it is difficult to control the well function of the cooling and/or lubrication during an on-going drilling operation due to the fact that the front tip of the drill bit at which a mouth of the fluid conduction is hidden inside the bore throughout the operation. Hence, the correct function of the cooling and/or lubrication may only be controlled indirectly by inspection of the bore or by running the drill bit in an open space and/or by inspecting the drill hole after a concluded drilling operation.
A problem that may occur with the fluid conduction is that the provision of fluid may vary over time, such that too much fluid is provided at times and such that too little fluid is provided at other times. A typical problem is that a large amount of fluid is provided at start-up of the machine followed by a phase where too little fluid is provided. At the end of an operation the fluid provision normally has stabilised such that a desired amount of mist is provided through the drill bit.
When too little fluid is provided the precision of the boring may be adventured and the drill bit and work piece may be over-heated. Too much fluid may also have a negative effect on the precision of the boring and further it implies that an excess of fluid will need to be washed away from the work piece.
Hence, there is a need of a drilling tool that does not have the problems of unreliable fluid conduction known in the art.